The long-term goal of this project is to assess the fall in glomerular filtration rate attributable to the commonly utilized therapy of parenteral iron in patients with chronic kidney disease (CKD). We hypothesize that in subjects with mild to moderate CKD, infusion of intravenous iron (MR) when compared to oral iron, will generate oxidative stress and cause an inflammatory response that will be associated with a more rapid decline in glomerular filtration rate (GFR) compared to oral iron. Comparison of IV iron with oral iron will allow testing the hypothesis that MR is injurious to the kidney. Specific aims: We will directly test the hypothesis that MR will generate an inflammatory response and albuminuria in the short-term, that will directly lead to a greater rate of fall in GFR, in the long-term, compared to oral iron. We hypothesize that after administration of one gram of IV iron over a course of 8 weeks, renal injury as documented by albuminuria (and fall in GFR) will be increased with IV iron sucorse therapy compared to those randomized to oral iron therapy. Methods: A randomized, parallel group, controlled trial will be performed. GFR will be measured every 6 months for two years in 200 participants by iothalamate clearances. Significance: Intravenous iron is commonly utilized and is likely a mechanism of renal injury in patients with CKD. Novelty and Health Relatedness of the Project: This proposal will provide translational data on the role of intravenous iron to progression of kidney disease in patients with CKD.